The invention concerns a multilayer headbox of a paper machine, notably the nozzle of a multilayer headbox. Such a headbox is known, e.g., from DE-OS 37 04 462.
In multilayer headboxes for the production of multilayer papers, the nozzle space is divided across the entire machine width by one or several fins which protrude out of the nozzle. The layers differ normally in the composition of the stock suspension, attempting for instance to produce papers which in their basic structure consist of recycled waste paper while the one-sided or double-sided cover layer consists of high-quality paper material. The stock suspension layers converge at the end of the fin and are dewatered in the follow-on former on or between the sheet formation wire(s). The objective is to produce a product with maximally high purity of layers, that is, without mixing between layers. That is, a paper is meant to be produced, e.g., which in terms of its surface qualities matches newly produced papers while the supporting center layer consists of recycled waste paper.
The installation of fins enlarges the friction surface between the stock suspension and the guide surfaces (fins, duct walls). With the prior headboxes, the turbulence energy becomes, due to friction, so high with increasing jet velocity that individual layers mix ever more heavily in the free jet, thereby affecting the quality of the paper produced. Furthermore, high turbulence gives rise to the possibility of droplets separating from the jet surface and leading, in the sheet formation, to disturbances in the paper.
The problem underlying the invention is to provide a multilayer headbox in which a minimally low mixing of individual layers takes place after or at the issuance out of the headbox nozzle, where it would be advantageous if the tendency for droplet formation at high velocities could as well be reduced.